Normalized abundances of six dominant atomic species N(X)/N(H_tot) vs. molecular fraction f(H₂) (a proxy for the local hydrogen density). The stars denote the sight line toward HD 62542: red = main (14 km s⁻¹) component; green = all other components; blue = all components. The other symbols are for sight lines in the Galactic ISM—mostly from Welty & Crowther (2010) for Ti II and from Jenkins (2009) for the other species. The solid lines represent weighted and unweighted fits to the trends for f(H₂) > 0.1 (not including the Sco-Oph or Trapezium sight lines); the upper horizontal dotted lines mark the protosolar photospheric abundances (Lodders 2003); the lower horizontal dotted lines give the average values for f(H₂) < 0.01. The declines in the normalized abundances for f(H₂) > 0.1 reflect increasingly severe depletions in denser gas, particularly for Mg, Ti, and Fe. The depletions of several of these elements are more severe than usual for some Sco-Oph sight lines (blue squares) and are even more severe in the main component toward HD 62542 (red stars).